Systems and methods for enhanced efficiency auxiliary power supply module

ABSTRACT

A power supply for use in a solar electric production system, including: a first stage having an input connected to a voltage from a photovoltaic panel and an output providing a first voltage different from the voltage from the photovoltaic panel; and a second stage connected to the output of the first stage, the second stage supplying power at a second voltage to a micro-controller, where the output of the first stage is turned on and stable for a period of time before the second stage is turned on to supply the power at the second voltage to the micro-controller.

RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 15/392,960, filed Dec. 28, 2016 and issued as U.S.Pat. No. 9,966,848 on May 8, 2018, which is a continuation applicationof U.S. patent application Ser. No. 14/822,227, filed Aug. 10, 2015, andissued as U.S. Pat. No. 9,584,021 on Feb. 28, 2017, which is acontinuation application of U.S. patent application Ser. No. 12/787,205,filed May 25, 2010 and issued as U.S. Pat. No. 9,143,036 on Sep. 22,2015, which claims the benefit of filing dates of U.S. Prov. App. Ser.No. 61/275,734, filed Sep. 2, 2009, and Prov. U.S. App. Ser. No.61/336,743, filed Jan. 26, 2010, the entire disclosures of whichapplications are hereby incorporated herein by reference.

FIELD OF THE TECHNOLOGY

At least some embodiments of this disclosure relate to photovoltaicsystems in general, and more particularly but not limited to, enhancingthe efficiency for auxiliary power supply modules used in photovoltaicsystems.

BACKGROUND

Typically, power supplies or power supply modules used for photovoltaicsystems may provide, for example, 3.3V to be used as a main supplyvoltage, in most applications when the photovoltaic system needs tomaintain low voltage for energy-saving purposes. However, when the powersupplies are driving the metal-oxide-semiconductor field-effecttransistors (MOSFET) or similar devices or switches contained within thephotovoltaic systems, the power supplies or power supply modules ofphotovoltaic systems may have to provide higher voltage levels such as,for example, 10V to 12V. Keeping the main supply of the control circuitand the overall power supply module at, for example, 3.3.V may bepreferable in order to maintain ideal energy-savings for the operationof photovoltaic systems.

SUMMARY OF THE DESCRIPTION

Systems and methods in accordance with the present disclosure aredescribed herein. Some embodiments are summarized in this section.

In one of many embodiments of the disclosure, provided is a power supplyfor use in a solar electric production system. The power supplyincludes: a first stage having an input connected to a voltage from aphotovoltaic panel and an output providing a first voltage differentfrom the voltage from the photovoltaic panel; and a second stageconnected to the output of the first stage, the second stage supplyingpower at a second voltage to a micro-controller, where the output of thefirst stage is turned on and stable for a period of time before thesecond stage is turned on to supply the power at the second voltage tothe micro-controller.

In another embodiment, provided is a power supply for use in a solarelectric production system. The power supply includes: a first stagehaving an input and an output, the input of the first stage to receivepower from a photovoltaic panel, the output of the first stage toprovide a first voltage different from the voltage received at the inputof the first stage; a switchable load; a second stage having an inputconnected to the output of the first stage, the second stage to supplypower at a second voltage to an micro-controller; and a control circuitto provide a signal to the switchable load to switch off the switchableload prior to providing a signal to the second stage to enable outputfrom the second stage to the micro-controller.

Other embodiments and features of the present disclosure will beapparent from the accompanying drawings and from the detaileddescription which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments are illustrated by way of example and not limitation inthe figures of the accompanying drawings in which like referencesindicate similar elements.

FIG. 1 shows an example gate charge vs. gate-to-source voltage diagramaccording to an embodiment of the present disclosure.

FIG. 2 shows a diagram illustrating RDSon behavior as a function of VGS(voltage between gate and source of a FET) according to an embodiment ofthe present disclosure.

FIG. 3 shows a schematic description of an auxiliary circuit accordingto an embodiment of the present disclosure.

FIG. 4 shows a schematic description of a circuit practicing a systemand method according to an embodiment of the present disclosure.

FIG. 5 shows a schematic description of an example startup behavior ofwave forms, according to an embodiment of the present disclosure.

FIG. 6 shows a power supply according to one embodiment.

DETAILED DESCRIPTION

The following description and drawings are illustrative and are not tobe construed as limiting. Numerous specific details are described toprovide a thorough understanding. However, in certain instances, wellknown or conventional details are not described in order to avoidobscuring the description. References to one or an embodiment in thepresent disclosure are not necessarily references to the sameembodiment; and, such references mean at least one.

Provided is a system and method for an auxiliary power supply moduleused in a photovoltaic system to increase the efficiency of thephotovoltaic system and reduce maintenance responsibilities of thesystem, or housekeeping requirements, wherein housekeeping roughly meansthe energy, power or voltage requirements needed to operate controls andswitches of a photovoltaic system that converts sunlight intoelectricity, as well as to manage and control directly associated tasks,including but not limited to communication operations and so on. Thisincrease in efficiency and power savings may be achieved by designing aphotovoltaic system where the efficiency curve is as flat as possible.For example, in order to achieve such efficiency objectives, an internalauxiliary power supply having reduced power consumption may be used todrive the MOSFETs of a photovoltaic system at the lower power end of theefficiency curve in order to ultimately obtain the most efficient powersavings possible.

One application of the present disclosure is to power control circuitsfor a solar panel using the power generated by the solar panel. Forexample, a power supply module of one embodiment is used to power thelink module (200) using the electricity generated by the photovoltaicpanel (101 n) described in U.S. patent application Ser. No. 11/875,799,published now as U.S. Pat. App. Pub. No. 2008/0097655. For example, apower supply module of one embodiment is used to power the localmanagement unit (LMU) (101) using the electricity generated by the solarmodule (102) described in U.S. patent application Ser. No. 12/411,317,now issued as U.S. Pat. No. 7,602,080. In one embodiment, a sun can beshown along with any of the above-referenced Figures—illustrate that thesun may be the source of photovoltaic energy absorbed by a solar panel,for instance. The contents of the above discussed patent and publicationare incorporated herein by reference.

FIG. 1 shows an example gate charge vs. gate-to-source voltage diagramaccording to an embodiment of the present disclosure. Gate charge (QG)vs. gate-to-source voltage (VGS) diagram (100) comprises at least onedrain-to-source voltage (VDS) curve (102), a gate-to-source voltage(VGS) axis (104), having a unit of measurements of Volts, and a totalgate charge (QG) axis (106), having a unit of measurement of Coulombs,or capacitive charge, or in the specific case of FIG. 1, nano-Coulombs(nC).

FIG. 1 analyzes the gate, drain and source of a typical MOSFETtransistor that may be used in a photovoltaic system, for example.According to an embodiment of the present disclosure, driving the gateof the MOSFET relative to the source with a lower voltage value (low VGSvalues on the gate-to-source voltage axis (104)) may yield energysavings for the associated voltage drive at, for example, saving roughlytwice the amount of energy compared to using high-voltage values). Notealso that the slope (change in gate-to-source voltage over change intotal gate charge) is slightly higher for lower values of VGS as opposedto higher values of VGS, which may mean greater power efficiencyoverall. Both the lowered voltage of the gate-to-source voltage VGS andthe lowered internal gate capacity (which in turn reduces the charge ordischarge current across the gate) result in a roughly quadratic savingsof power. This power savings allows a photovoltaic system to achievegreat reduction in housekeeping energy supply, by using an “adaptive”gate drive that adapts power consumption based on the amount of gatedriving voltage provided. Therefore, as can be seen in FIG. 1, thereduction in gate charge is linear in relation to the gate-to-sourcevoltage VGS.

MOSFETs have a threshold input voltage, above which the transistor issubstantially in full conduction mode or in saturation mode. For safeoperation and full conduction, the minimum gate voltage should be atleast 1V above the minimum threshold voltage value. Even if fullsaturation is not achieved, particularly at the low end of the powerrange, a loss in switching efficiency may be small, whereas at the samelow end of the power range, housekeeping energy may suddenly become anissue. Adjusting the gate drive voltage is required to reduce theauxiliary supply current at low load conditions, whereas the effectiveresistance between the drain and the source of a MOSFET (RDS) has littleto no influence on switching efficiency. For a MOSFET above its turn-onthreshold voltage, the total gate charge value versus normal gate chargevalue is a straight line, as is well known in the art, meaning that thebehavior per each load current exhibits constant capacitance. Therefore,the gate drive current may behave according to ½CV²f, where C=theequivalent capacitance,V=the gate voltage, and f=operating frequency.Thus it is clear that reducing the gate voltage from 11V to 7V mayreduce the drive current by more than two orders of magnitude. At thesame time that the RDSon (the resistance between the drain and thesource of a MOSFET switch (or other FET switch) when fully on) isincreased by less than 1.5 times its 12V value. At light load conditions(less than 30 percent of a standard-rated load) the change in RDSon doesnot affect the overall efficiency of the overall MOSFET transistor or ofthe photovoltaic system.

FIG. 2 shows a diagram illustrating RDSon behavior as a function of VGS(voltage between gate and source of a FET) according to an embodiment ofthe present disclosure. Drain-to-source voltage (VDS) to drain-to-sourceCurrent (ID) diagram (200) comprises at least one gate-to-source voltage(VGS) curve 202, a drain-to-source Current (ID) axis 204, and adrain-to-source voltage (VDS) axis 206. As can be seen from FIG. 2, agate-to-source voltage value (VGS) between 15V to 6V does not affect theresistance significantly up to a 1V drop which is the range of RDSon(the resistance between the drain and the source of a MOSFET when fullyon) for the switching area. The resistance is not effected significantlyup to a 1V drop because the MOSFET is in saturation mode, and becauseVDS=I*RDSon and RDSon is a function of both VGS and VDS, so when VGSchanges, the RDSon value is affected. As also can be observed from FIG.2, the slope (change in ID over change in VDS) increases for highervalues of VGS and begin to decrease and plateau for lower values of VGS.This implies that there is an optimal VGS value to drive the gatevoltage at in order to still be efficient and not affect the range ofRDSon, which is desired in order to avoid any excessive powerconsumption from the resistance of RDSon.

Further details about characteristics of MOSFETs in one embodiment(e.g., used as switches for controlling the output of solar panels) maybe provided in IRF8101E/S/SLPbF data sheet from International Rectifier,which is hereby incorporated herein by reference.

FIG. 3 shows a schematic description of an auxiliary circuit accordingto an embodiment of the present disclosure. Auxiliary circuit (300) is acircuit designed to control the auxiliary power for a photovoltaicsystem, for example. In one embodiment, the auxiliary circuit (300)receives in the input terminal (333) electricity from the photovoltaicpanel (101 n) described in U.S. patent application Ser. No. 11/875,799,or from the solar module (102) described in U.S. patent application Ser.No. 12/411,317. In one embodiment, the auxiliary circuit (300) providesin one output terminal (330) a voltage for control logic, such as thelink module (200) described in U.S. patent application Ser. No.11/875,799 or the controller (109) described in U.S. patent applicationSer. No. 12/411,317. In one embodiment, the circuit (300) provides inone output terminal (331) a voltage for driving a switch, such as aswitch having characteristics shown in FIGS. 1 and 2, which can be usedas a switch in the link module (200) described in U.S. patentapplication Ser. No. 11/875,799, or a switch (106) and/or a switch (108)described in U.S. patent application Ser. No. 12/411,317.

In one embodiment, the auxiliary circuit (300) includes step-downconverters, such as a buck converter (301) to drive a first voltageoutput (331) and a buck converter (311) to drive a second voltage output(330). The auxiliary circuit (300) uses capacitor (326) as a backuppower supply in order to keep buck converter (311) running longer thanbuck converter (301). In other words, capacitor (326) is charged by buckconverter (301) and used by buck converter (311) as a power supply suchthat the output of buck converter (311) lasts longer than the output ofbuck converter (301). If the output of buck converter (301) is out orunstable for a little while, buck converter (311) can still keep theauxiliary circuit (300) working properly at 3.3V for this short periodof power outage or instability. Thus, the control logic powered by thevoltage (330) will have enough power to provide appropriate controlsignals, until the drive stage powered by the voltage (331) loses thepower (e.g., to operate the switch for the solar panel). Utilizingcapacitor (326) may be beneficial in situations where the solar panel istemporarily out of power, such as, for example, when the solar panel iscovered by a falling leaf or a bird flying by or a brief shadow.

In one embodiment, auxiliary circuit (300) has input voltage (333), buckconverter (301), voltage (332), MOSFET (345), drive voltage (31),resistor (319), resistor (313), capacitor (326), buck converter (311),3.3.V logic supply output (330), diode (322), resistors (323, 324, 325),transistors (320, 321), control block (315), and resistors (341, 342,343, 340). The buck converter (301) has: MOSFET (302), diode (305),inductor (306), resistors (308, 309, 310), capacitor (307), MOSFET(303), and control (304). The buck converter (311) has: MOSFET (312),diode (325), inductor (327), capacitor (328) and control (314). Variousknown converters can be used to replace the voltage conversion portionof the buck converters (301 and 311), such MOSFET (302), diode (305),inductor (306) and capacitor (307) in the buck converter (301), orMOSFET (312), diode (325), inductor (327) and capacitor (328) in thebuck converter (311). Therefore, the details shown in buck converter(303) and buck converter (311) are merely illustrative, and other typesof buck converters known in the art may be used. In one embodiment,control block 315 has: control circuit (318), and transistors (317,316). The control circuits 304, 314 and 318 may be interconnected viaone or more control signals or connected to one source, such as amicro-controller, although this embodiment is not explicitly shown inFIG. 3. In one embodiment, the control circuit (318) controls theoperations of the control (304) and control (314).

In auxiliary circuit (300), drive voltage (331) is controlled by aserial MOSFET (345) and resistor (319). Before enabling the serialMOSFET (345), transistor (321) is to be turned on by meeting at leastthe following two conditions: (i) 3.3V logic supply (330), for example,is on and higher than at least, for example, 2.6V. (ii) At thisparticular voltage level, the threshold formed by Zener diode (322) andresistors (324) and (325), as well as when the VBE (base-emittervoltage) of transistor (321) (if transistor (321) comprises a bipolartransistor instead of a MOSFET) activates transistor (321), thus makingthe control circuit (318) operative and able to control transistor (316)to change from open collector to conductive or on (if transistor (316)is a bipolar transistor, for example). Resistor (323) further enablesthe 3.3V logic supply (330), for example, to be used in operation withtransistor (320) (transistor (320) shown as being a bipolar transistorin FIG. 3). According to an embodiment of the present disclosure, aMOSFET is used instead of a bipolar transistor for some or all of thebipolar transistors (e.g. (321), (316), (320)) shown in FIG. 3 andthroughout the present disclosure. Voltages and/or resistors can beadjusted for the use of MOSFETs, instead of bipolar transistors, toproperly accommodate such substitution. In one embodiment, the enablecircuit (320, 321, 322, 323, 324, 325, 345, 319) connects the output ofbuck converter (301) to its load (e.g., MOSFET switches, see descriptionbelow for FIG. 4) only when the 3.3V output is stable and above a 2.6Vthreshold, for example.

Transistor (316) and control circuit (318) are both internal to controlblock (315), the control circuit (318) being naturally defined bydefault in the “open drain” state when turned on. When theabove-described two conditions are met, transistor (321) enables MOSFET(345) to turn on the drive voltage to power the Vi for the drive stageoutput (331). That is, in other words, drive stage output (331) may notactually receive a drive voltage when the control circuit is notoperating. The control circuit may disable the drive voltage duringother conditions, such as a low output voltage from buck converter (301)sensed by resistors (340) and (341) and connected to control circuit(318). Buck converter (301) may yield a wide range of voltage for theinput voltage (333). Buck converter (301) also is controlled by control(304) and feedback from transistor (303). Resistors (342) and (343)connect the input voltage (333) to transistor (302), and the node inbetween the middle of resistors (342) and (343) may be directlyconnected to the control circuit (318) of control block (315). Low logicvoltage may shut-down the voltage for the drive stage output (331). Awide operation range may be easily achieved by buck converter (301). Thebuck converter (301) may also be turned on when the input voltage (333)is above 6.5V, for example (at turn on, buck converter (301) is notrequired to regulate anything, and may just have an output voltage thatis higher than 5V, for example).

In one embodiment, transistor (316), transistor (320), transistor (321),diode (322), resistor (323), resistor (324), resistor (325), resistor(319) and transistor (345) are configured to ensure that transistor(345) is turned on only when voltage supply (330) is high enough andwhen control circuit (318) is working properly (e.g., ready and/orsending the proper signals). Transistor (321) will turn on when (I)voltage supply (330) is at an adequate level and (II) when controlcircuit (318) is working properly (e.g., ready and/or sending propersignals). First, transistor (321) may turn on only when voltage supply(330) is on and higher than, for example, 2.6V. At this voltage levelthe threshold formed by diode (322) and resistors (324) and (325), aswell as the VBE (base-emitter) voltage of transistor (321) activatestransistor (321), if transistor (320) is not turned on. Second, ifcontrol circuit (318) is operative or working properly, it will providea high voltage to the base or gate of transistor (316) to turn ontransistor (316). Transistor (316) may be the internal part of controlcircuit (318) with an open collector or open drain. When transistor(316) is on, transistor (320) is off, which prevents transistor (321)from being turned off if the voltage supply (330) is high enough (e.g.,above 2.6V). When transistor (316) is turned off because control circuit(318) is not working properly for lack of power or simply not ready, andwhen logic supply (330) is high enough, resistor (323) is able to turntransistor (320) on. Once transistor (320) is on, the gate or base oftransistor (321) is connected to the ground via transistor (320); andthus transistor (321) turns off, which in turn turns off transistor(345).

When the above described two conditions (I and II) are both met,transistor (321) is turned on to allow transistor (345) to turn on thedrive voltage to drive the “Vi to drive stage” output (331). Whentransistor (321) turns off, the resistor (319) is not sufficient to turnon transistor (345) and thus the “Vi to drive stage” output (331) isdisabled by the transistor (345).

In one embodiment, when (a) voltage supply (330) becomes high enough, atfor example above 2.6V and (b) control (318) is not working properly toturn on transistor (316), the voltage level after dropping past resistor(323) is high enough to feed into the base or gate of transistor (320),which then is able to turn transistor (320) on or put it in saturationmode. Transistor (320) may be turned on only if transistor (316) is off,which indicates that the control circuit (318) is not ready. In such acase where the transistor (320) is turned on in saturation mode, thebase or gate of transistor (320) is connected to ground via thetransistor (316) in saturation mode. When transistor (320) is on, avoltage near a ground value is sent to the gate or base of transistor(321) via transistor (320), therefore turning transistor (321) andtransistor (345) off (since the control circuit (318) is not be ready,as indicated by the state of transistor (316)). In one embodiment,transistor (316) serves as a switch to toggle transistor (320). Iftransistor (316) is turned off, as discussed above, transistor (320) maybe on if the voltage supply (330) is high enough. Likewise, iftransistor (316) is turned on, a ground value is fed into the base orgate of transistor (320), therefore turning transistor (320) off. In oneembodiment, transistor (316) is controlled by control circuit (318) toindicate the readiness of the control circuit (318). When ready, controlcircuit (318) provides a high enough voltage to the base or gate oftransistor (316) to turn it on.

When transistor (321) is on, transistor (345) is on if the output (332)from the converter (301) is high enough. Likewise, if transistor (321)is off, transistor (345) is off even if the output (332) is high enough(for the lack of a sufficient voltage drop across bias resistor (319)).In one embodiment, transistor (345) is always off until the voltage dropacross resistor (319) increases to turn transistor (345) on (e.g., whenoutput (332) is high enough and transistor (321) is on for a connectionto ground). In one embodiment, the transistor (345) is a PMOS transistoror a PNP bipolar junction type of transistor. In one embodiment, asufficient voltage drop across resistor (319) from logic supply (332) isprovided by transistor (321) turning on and therefore connecting thegate of transistor (345) to ground.

In one embodiment, the input voltage of buck converter (301) is betweenthe input voltage (333) and the ground located at the bottom of thediode (305) and the capacitor (307). The output voltage of buckconverter (301) is between the voltage (332) and the same ground locatedat the bottom of the diode (305) and the capacitor (307). Changing theduty cycle of MOSFET (302) changes the output voltage of buck converter(301). Control circuit (304) of buck converter (301) controls the dutycycle of buck converter (301) by controlling the gate of MOSFET (302).The input voltage of buck converter (311) is between the voltage on thenode just above the capacitor (326) and the ground located at the bottomof the diode (325) and the capacitor (328). The output voltage of buckconverter (311) is between the voltage on (330) and the same groundlocated at the bottom of diode (325) and the capacitor (328). Like buckconverter (303), the control circuit (314) of buck converter (311)controls the duty cycle of buck converter (311) by controlling the gateof MOSFET (312).

The buck converter (311) is operative from 5V to 20V, for example. Thus,if input loss conditions are experienced, buck converter (311) is thelast unit to turn off running from bypass capacitor (326) while buckconverter (301) cannot regulate the circuit/system or is in off mode.The buck converter (311) also runs off control circuit (314), thecontrol circuit (314) working in tandem with transistor (314) toeffectively control buck converter in a feedback mechanism. Furthermore,in one embodiment, the auxiliary circuit (300) is to identify low powerconditions and reduce buck converter (301) voltage from 11V to 7V, forexample, by transistor (317), which may in turned be controlled bytransistor (303), transistor (303) being able to control the buckconverter (301) set point or ideal operating point by means of controlcircuit (304). When the control circuit identifies low power conditions,it may set transistor (317) on, which results in transistor (303) goingoff and voltage (332) being set to a low operation drive voltage(typically 7V, for example, which is the lowest power consuming modevoltage of the overall control circuit). MOSFET (303) also effectivelyserves as a switch to selectively lower the voltage output of buckconverter (303) from 11V to 7V, for example. For most low voltageMOSFETS, two levels of drive voltage may be enough, but additionallevels are possible.

One of the problematic aspects of operating a controller in a solarpower environment is the unreliability of the power source during theearly morning hours as well as during late evening hours, when faintblue light allows the panel to generate a high voltage, but presentsbarely enough current to properly operate. As a result, circuits oftencreate a “false start” in which the voltages appear to be there, but assoon as the controller becomes active there is a drop or brown out orpower outage, leading to the undesirable occurrence of unstable or evenmeta-stable modes, which may occur more frequently for small processors.

FIG. 4 shows a schematic description of a circuit practicing a systemand method according to an embodiment of the present disclosure. Circuit(400) is another circuit that may be used as an auxiliary power supplyor power supply module for a photovoltaic system, for example. In oneembodiment, circuit (400) uses control logic to ensure that solar poweris strong enough to enable output from the buck converter (402). Preloadresistor P1 (405) is used to emulate the load of buck converter (402).If the output of buck converter (401) can support the load, the preloadresistor P1 (405) is disconnected and the output of the buck converter(402) is connected to its load. Circuit (400) therefore can be used toaddress the false start problem that occurs when the solar panel is ableto provide enough output voltage when it is not connected to the output,but not enough to sustain even a small current provided by the buckconverter (402) to its load, such as a control logic, a control circuit,a micro-controller, etc.

In one embodiment, when the intermediate housekeeping voltage Vbuck1(i.e., the voltage to operate an auxiliary microcontroller unit or MCU)is turned on by buck converter (401), Vbuck1 is initially used to powera preload resistor P1 (405), by turning on the switch (404), typically aFET or bipolar transistor controlled by one of the outputs of delaycircuit (403) (also supplied by Vbuck1 but not shown here for clarity).The other output of delay circuit (403) suppresses at the same time buckconverter (402). After the housekeeping voltage Vbuck1 is above apredefined threshold for the full delay period of delay circuit (403),the switch 404, and thus the preload resistor P1, is turned off toprovide power for the load of the buck converter (402) and the 3.3Vlogic is permitted to turn on and output from buck converter (402) inaccordance with the enable signal from the delay (403).

Here, in FIG. 4, Vbuck1 is shown having an ideal range of 10-11V, forexample, but this range has been merely provided for exemplary purposesand should not be taken to limit the disclosure to any particular range.This approach provides a smooth turn-on of the logic voltage. Typically,the load of resistor P1 (405) should exceed the load of buck converter(402) (buck converter's load being the MCU which is not shown), so thatactivating buck converter (402) does not crash the housekeeping voltageVbuck1. Otherwise, the system of the circuit (400) might experienceturn-on attempts which could not be completed, and as a result, the MCUcould get stuck due to meta-stability effects of the MCU in some casesand some of the time.

In one embodiment, the loading of this approach is slightlyunpredictable; and positive hysteresis is introduced in order to preventoscillations. For instance, amplifier (406) may be used as a VHV (veryhigh voltage) monitor in order to perform positive hysteresis toultimately avoid oscillations. The reason this hysteresis modificationis used is that at very low light conditions (where the sunlight is verydim for instance), solar panels can provide voltages that are highenough for turning on, but cannot ultimately provide sufficient powerfor the circuit that is to be powered by the buck converter (402).Therefore, identifying a simple threshold for voltage Vbuck1 does notstop unsuccessful turn-on attempts, if no hysteresis is employed indelay circuit (403) (meaning the delay starts only if Vbuck1 is, forexample, at least 1.2 times the minimal input voltage of buck converter(402)). One way to prevent such attempts is to permit the system ofcircuit (400) to turn on only when it can stay on with the availablegiven power. Power is measured by measuring the voltage on resistor P1(405) (plus any losses from the switch (404)) as represented by Vbuck1.In one embodiment, the delay circuit (403) can be omitted from thecircuit (400), since this approach can also work with zero delay becauseof positive hysteresis. The above-described approach improves theperformance of an electronic device mounted on a panel and a devicehaving a MCU or a device similar to a MCU. The buck converter (401) partshould be able to accept any variation in voltage during turn-on becauseit may not be sensitive.

In the above FIGS. 3-4, the voltage conversion section of the buckconverters (e.g. 401, 402, 301, or 311) can be replaced with step-downconverters or other converters known in the art.

In one embodiment, the features illustrated in FIG. 3 can also be usedin the circuit in FIG. 4. For example, the enable circuit (320, 321,322, 323, 324, 325, 345, and 319) in FIG. 3 can be used in the circuitof FIG. 4 to control the output of the voltage Vbuck1 to a drive stagevia MOSFET (345). For example, a capacitor can be connected to the inputof the buck converter 402 in FIG. 4, in a way as the capacitor 326connected to the input of the buck converter 311 in FIG. 3. For example,the control block 318 used to control the enable circuit in FIG. 3 canalso be used in the circuit of FIG. 4; and the circuit (317, 303,308-310) and control block (304) in FIG. 3, used to reduce outputvoltage of the buck converter 301 when the input power from the solarpanel is low, can also be used to control the output voltage of the buckconverter (401) in FIG. 4. For examples, the resisters 340-343 connectedto input and output of the buck converter 301 in FIG. 3 to detect lowpower conditions in FIG. 3 can also be used for the buck converter 401in FIG. 4.

One application of the present disclosure is using the high voltagesfrom buck converter (e.g. 301 or 401) (e.g. Vbuck1) to control MOSFETswitches used in a solar panel energy system and the low voltage frombuck converter (e.g. 311 or 402) can be used to power control circuitsfor a solar panel using the power generated by the solar panel. Examplesof the MOSFET switches can be found in at least U.S. patent applicationSer. No. 12/366,597, published as U.S. Pat. App. Pub. No. 2009/0133736,and U.S. patent application Ser. No. 12/411,317, now issued as U.S. Pat.No. 7,602,080, all the contents of which are incorporated herein byreference. Examples of the control circuits can be found in at leastU.S. patent application Ser. No. 11/875,799, published now as U.S. Pat.App. Pub. No. 2008/0097655, and U.S. patent application Ser. No.12/411,317, now issued as U.S. Pat. No. 7,602,080, the contents of whichare incorporated herein by reference.

FIG. 5 shows a schematic description of an example startup behavior ofwave forms, according to an embodiment of the present disclosure. Waveforms (500), where the x-axis is time, may be generated from running thecircuit (400) shown in FIG. 4, above, through simulations. Curve (501)may represent the Vin (or input voltage value) from the solar panel intobuck converter (401). Curve (502) may represent the output of buckconverter (401), which is Vbuck1 as shown in FIG. 4. Curve (503) mayrepresent the power used from the panel. Note in FIG. 5 the drop ofpower at dotted line (505) when the photovoltaic system is turned on. Atdotted line (505), the second stage is turned on and therefore thesystem is turned on. Curve (504) may represent the output of delaycircuit (403) controlling switch (404) and curve (506) may represent theVB2E value coming out of delay circuit (403) ultimately used to controlbuck converter (402). Also, Curve (504) may show that the preloadresistor P1 (405) may be turned off after Vbuck1 passes a designatedthreshold level and a delay time has passed.

It is clear that many modifications and variations of this embodimentmay be made by one skilled in the art without departing from the spiritof the novel art of this disclosure. These modifications and variationsdo not depart from the broader spirit and scope of the presentdisclosure, and the examples cited here are to be regarded in anillustrative rather than a restrictive sense.

The performance of solar modules can vary significantly withtemperature. A system capable of measuring temperature can implementmethods for controlling the voltage, power output, or the efficiency ofone or more strings of solar module controllers using module temperatureas a factor. For example, a formula presented by Nalin K. Gautam and N.D. Kaushika in “An efficient algorithm to simulate the electricalperformance of solar photovoltaic arrays,” Energy, Volume 27, Issue 4,April 2002, pages 347-261, can be used to compute the voltage of a solarmodule at the maximum power point. Other formulae can also be used.

Many variations can be applied to the above disclosed systems andmethods, without departing from the spirit of the present disclosure.For example, additional components can be added, or components can bereplaced. For example, rather than using a capacitor as primary energystorage, an inductor can be used, or a combination of inductor andcapacitor. Different types of transistors—such as MOSFET or bipolartransistors—may also be used interchangeably, with appropriateadjustments to voltage and other settings. Also, the balance betweenhardware and firmware in the micro controllers or processors can bechanged, without departing from the spirit of the present disclosure.

It is clear that many modifications and variations of this embodimentcan be made by one skilled in the art without departing from the spiritof the novel art of this disclosure. For example, the systems and methodherein disclosed can be applied to energy generating systems besidessolar photovoltaics (e.g., windmills, water turbines, hydrogen fuelcells, to name a few). Also, although specific voltage values andthresholds have been mentioned, other reference points for the targetvoltage can also be used. These modifications and variations do notdepart from the broader spirit and scope of the present disclosure, andthe examples cited here are to be regarded in an illustrative ratherthan a restrictive sense.

In the foregoing specification, the disclosure has been described withreference to specific exemplary embodiments thereof. It will be evidentthat various modifications can be made thereto without departing fromthe broader spirit and scope as set forth in the following claims. Thespecification and drawings are, accordingly, to be regarded in anillustrative sense rather than a restrictive sense.

What is claimed is:
 1. An apparatus, comprising: a micro-controller; afirst stage power converter to generate a first output from a directcurrent input; a switchable load powered by the first output; a controlcircuit powered by the first output; and a second stage power converterconnected to the first stage power converter and configured to convertthe first output to a second output; wherein the control circuit isconfigured to block the second stage power converter from powering themicro-controller using the second output in a time period that is afterthe control circuit is powered by the first output and before apredefined condition is met in the control circuit; and wherein thecontrol circuit is configured to signal the switchable load to be in afirst state of consuming the first output during the time period and tobe in a second state of not consuming the first output after the timeperiod.
 2. The apparatus of claim 1, wherein the predefined conditionincludes a voltage of the first output reaching a threshold.
 3. Theapparatus of claim 1, wherein, when the switchable load is in the secondstate, the voltage above the threshold is sufficient to power the secondstage power converter to operate the micro-controller for at least apredetermined period of time during which the direct current input tothe first stage power converter has diminishing power.
 4. The apparatusof claim 1, wherein the switchable load comprises: a resistive device;and a switching device connected to the resistive device, wherein theswitching device is turned on in the first state to connect theresistive device to the first output and turned off in the second stateto disconnect the resistive device from the first output.
 5. Theapparatus of claim 1, wherein the control circuit delays a first signalinstructing the switching device to change from the first state to thesecond state to generate a second delayed signal that instructs thesecond stage power converter to change from not powering themicro-controller to powering the micro-controller.
 6. The apparatus ofclaim 5, wherein the control circuit comprises: a hysteresis amplifiercoupled to the first output to generate the first signal; and a delaycircuit coupled to the first signal to generate the second delayedsignal.
 7. A method to supply power, the method comprising: generating,by a first stage power converter, a first output from a direct currentinput; powering a control circuit using the first output; generating, bya second stage power converter connected to the first stage powerconverter, a second output from the first output from the first stagepower converter; blocking, by the control circuit during a time periodthat is after the control circuit is powered by the first output andbefore a predefined condition is met in the control circuit, the secondoutput from the second stage power converter from powering amicro-controller; consuming, by a switchable load in a power absorptioncircuit, a portion of the first output from the first stage powerconverter during the time period; powering the micro-controller usingthe second output from the second stage power converter after the timeperiod; and stopping, by the control circuit and after the time period,the switchable load from consuming the first output from the first stagepower converter.
 8. The method of claim 7, wherein the predefinedcondition includes a voltage of the first output reaching a threshold.9. The method of claim 7, further comprising: signaling, by the controlcircuit, the switchable load to be in a first state of consuming theportion of the first output during the time period; and signaling, bythe control circuit, the switchable load to be in a second state of notconsuming the first output from the first stage power converter afterthe time period.
 10. The method of claim 9, wherein, when the switchableload is in the second state, the voltage above the threshold issufficient to power the second stage power converter to operate themicro-controller for at least a predetermined period of time duringwhich the direct current input to the first stage power converter hasdiminishing power.
 11. The method of claim 9, wherein the switchableload includes a resistive device, and a switching device connected tothe resistive device; wherein the method further includes: turning onthe switching device to place the switchable load in the first state inwhich the resistive device is connected to the first output; and turnedoff the switching device to place the switchable load in the secondstate in which the resistive device is disconnected from the firstoutput.
 12. The method of claim 9, further comprising: delaying, by thecontrol circuit, a first signal instructing the switching device tochange from the first state to the second state; and generating, via thedelaying, a second delayed signal that instructs the second stage powerconverter to change from not powering the micro-controller to poweringthe micro-controller.
 13. The method of claim 12, further comprising:generating the first signal using a hysteresis amplifier coupled to thefirst output.